Examples of devices currently used in spontaneously breathing anaesthetized patients, during recovering after anaesthetics, weaning of a certain group of patients in intensive care, or during resuscitation to provide a clear and hands-free airway are:—    a) Guedel airway with various types of face masks.    b) Cuffed Oro-pharyngeal airway.    c) Laryngeal Mask Airway (LMA), reinforced LMA, intubating LMA and a modified Intavent LMA for ENT and dental anaesthesia.    d) Airway Management device.    e) Combi-tube.    f) Self-retaining nasopharyngeal airway.    g) Cuffed or non-cuffed Endotracheal tubes, R.A.E. endotracheal tube.    h) Supraglottic oropharyngeal airway.    i) Tracheostomy and mini-trache tubes.    j) etc etc
All of the above mentioned devices carry significant and varying degrees of co-morbidity involving not only unacceptable concurrent physiological changes but also temporary and/or permanent anatomical/structural damage. Many cases of mortality caused directly or indirectly as a result of the use of such devices have also been reported.
Probably the most successful design variant is the inflatable laryngeal airway device, variants of which have been used to administer anaesthetic gases since 1988.
A brief history of the development of such airway device is described in a review by A I J Brain in the European Journal of Anaesthesiology 1991, Supplement 4, pages 5 to 17 inclusive. The entire text of this review is hereby incorporated by reference and is intended to form an integral part of this disclosure.
If the respiratory tree is seen as a tube terminating at the glottis, and the objective is to make a simple connection between this tube and an artificial tube for supplying gas under low pressure to the bronchial tree, it would seem logical to form a direct end-to-end junction between the two tubes. The face mask forms an end-to-end junction indeed, but with the wrong orifice, while the endotracheal tube meets the correct orifice but goes too far by penetrating into the lumen, so that the junction is effected within it, instead of at its rim. The undesirable aspects of intubation of the trachea result from the fact that, to effect a seal, pressure is applied to an epithelial surface whose important and highly specialized functions are thus compromised and that by penetration of the vocal cords, effective coughing is rendered impossible, upper-airway architecture is distorted and unwanted reflex response are not only provoked by laryngoscopy needed prior to intubation but also by presence of endotracheal tube in the trachea. Such laryngeal masks have been used in anaesthetic practice since and many reports of co-morbidity and/or mortality directly or indirectly related to their use have been reported. Complications and/or morbidity are caused by hyperinflation and extraluminal pressure impact onto the soft tissue and cartilagenous structures in contact with the hyperinflated cuff.
Several attempts have been made to improve this type of airway device but they still suffer from a number of serious inherent drawbacks. Firstly, they require inflation of the cuff to be effective and furthermore anaesthetic gas (nitrous oxide) can diffuse into the cuff, expanding the air in the cuff, thus increasing the cuff's extraluminal pressure significantly, and as a result, put considerable pressure on the sensitive tissues of Laryngopharynx. Secondly, these masks have a tendency to move from side to side or rotate about their longitudinal axis as a force is applied to the proximinal end of the tube, attached to the anaesthetic equipment. It will be appreciated that if such a device is to lie perfectly symmetrically in use then the airway tube will be aligned with the patient's nose. However, any rotational or sideways movement of the airway tube will have the potential to affect the seal that the airway device makes around the laryngeal inlet.
Several types of airway device have been described in the patent literature. For example, U.S. Pat. No. 5,976,072 (Johns Hopkins University) describes a fiberoptic endotracheal intubation device. However, this relies on an inflatable oro-pharyngeal cuff that suffers from the disadvantages referred to above.
U.S. Pat. No. 5,865,176 (O'Neil) and GB2,319,182 (VBM Medizintechnik GmbH) describe airway devices having a double inflatable cuff arrangement, a first inflatable cuff for providing a seal in the patient's pharynx and a second inflatable cuff for providing a seal in the patient's oesophagus. This arrangement compounds the problem of tissue damage as set out above.
In a contrasting arrangement, GB2,373,188 (Smiths Group plc) describes an inflatable laryngeal mask with a tear-shaped blocker plate designed to prevent the mask blocking the epiglottis during insertion. This only goes to emphasise the potential downsides of a tubular inflatable mask of this type.
Finally, in WO00/61213 (Brain) there is described a disposable laryngeal mask airway device with an inflatable cuff. However, not only does this suffer from all the disadvantages of an inflatable cuff device, but it is formed from multiple components, adding to the cost and complexity of manufacture.
Collectively, these represent the closest prior art known to the applicant.
It is an object of the present invention to overcome or mitigate some or all of these problems.
It is a further object of the present invention to provide an airway device that is both simple and effective to use and cost-effective to manufacture.
Where a single use item is concerned, cost of manufacture, and minimising this cost, is important. A further objective of the present invention is therefore to provide cost-effective methods for manufacturing airway devices that enable the unit cost per item to be minimised.
It is also an object of this invention to satisfy the requirements of clinical situations where a buccal cavity stabiliser would not enhance, but impede the operation. For example in many ophthalmalogical, and maxillofacial or dental surgery situations the use of a reinforced tube is preferable, as the tube can flexibly moved to one side to continue to provide an airway for the patient, whilst not interfering with the operation.
In summary, where it might be advantageous to have an airway device with a buccal cavity stabiliser in some applications, we have discovered that there are several applications where this is disadvantageous. In fact there are several applications where it is just not practical to have a buccal cavity stabiliser.